Non-staining polymer composite product

ABSTRACT

A polymeric composite is provided which has improved stain preventative properties by virtue of inclusion of at least one compound having multiple functional groups capable of reacting with tannins contained in a tannin containing cellulosic material present in the composite, and a method for its production and prevention of water stains thereon.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a polymeric composite product thatresists staining when contacted with moisture, and a method for itsproduction.

2. Discussion of the Background

Lumber, particularly decking lumber, is a multi-billion dollar industry.In the decking lumber industry alone, there are over 30 million existingdecks in the United States, with 3 million decks being built, repairedor replaced every year. One primary type of lumber used in the deckingindustry is pressure treated wood, typically made by impregnating thewood with a composition containing, among other things, arsenic underhigh pressure.

Synthetic lumber has been used as a substitute for wood, particularly inareas where wood can deteriorate quickly due to environmentalconditions. Modern recycling techniques and low cost extrusion processeshave greatly increased the market for such synthetic lumber products.

One synthetic alternative to pressure treated wood that has arisen iscomposite lumber, generally defined as any blend of plastics and wood orother natural fibers. Composite lumber is rapidly becoming the preferredalternative to pressure treated wood, with the market for composite andplastic lumber growing at an annual rate of 11%, with that rateestimated to continue for the next decade. The composite lumber productsare preferred over pressure treated wood due to toxicity reasons, aswell as the lower maintenance required for composite or plastic productsrelative to wood decking.

Unfortunately, conventional composite lumber products are not withouttheir drawbacks also. One of the most significant problems associatedwith conventional composite lumber is that of staining when the productis contacted with moisture. There is a need in the industry for acomposite lumber product that retains the advantages of conventionalproducts but which does not show water-spots or staining when contactedwith water and allowed to dry.

SUMMARY OF THE INVENTION

Accordingly, one object of the present invention is to provide acomposite lumber composition that does not exhibit staining whencontacted with moisture.

A further object of the present invention is to provide a method forpreparing a composite lumber composition having consistency ofappearance and that avoids staining.

These and other objects of the present invention have been satisfied bythe discovery of a polymeric composite product comprising about 35-75 wt% of a resinous material, about 25-65 wt % of a tannin containingcellulosic fiber material, calcium carbonate and an amount of a stainpreventive agent sufficient to suppress leaching of tannins from thecellulosic material upon application of moisture to a surface of theproduct.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein;

FIG. 1 provides structures for various compounds found in oak tannins(structures from J.-L. Puech et al, “The Tannins of Oak Heartwood:Structure, Properties, and Their Influence on Wine Flavor”,International Symposium on Oak in Winemaking/Am. J. Enol. Vitic., Vol.50, No. 4, pp 469-478 (1999)).

FIG. 2 provides structures for additional compounds found in oak tannins(structures from J.-L. Puech et al, “The Tannins of Oak Heartwood:Structure, Properties, and Their Influence on Wine Flavor”,International Symposium on Oak in Winemaking/Am. J. Enol. Vitic., Vol.50, No. 4, pp 469-478 (1999)).

FIG. 3 provides structures for various tannin chemical precursors(structures obtained from Cornell University animal science website,www.ansci.Cornell.edu).

FIG. 4 shows the results of water staining tests on PVC/oak flourcompositions containing various levels of calcium carbonate.

FIG. 5 shows the results of water staining tests on PVC/oak flourcompositions containing various levels of calcium carbonate, to whichvarious levels of succinic anhydride have been added.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to a polymeric composite productcomprising about 35-75 wt % of a resinous material, about 25-65 wt % ofa tannin containing cellulosic fiber material, calcium carbonate and anamount of a stain preventive agent sufficient to suppress leaching oftannins from the cellulosic material upon application of moisture to asurface of the product.

The polymeric composite product of the present invention is a compositeof about 35-75 wt % of resinous materials, such as thermoplastic orthermosetting resins. Suitable resinous materials include, but are notlimited to, polyvinyl chloride (PVC), polyethylene, polypropylene,nylon, polyesters, polysulfones, polyphenylene oxide, polyphenylenesulfide, epoxies, cellulosics, and mixtures or blends thereof. Theresinous material of the present composition may be virgin material orcan be obtained by recycling resinous materials from any of a variety ofsources. The resinous material of the present invention can bewater-white or pigmented as desired.

The resinous material is most preferably PVC. PVC thermoplasticscomprise the largest volume of thermoplastic polymers in commercial use.Vinyl chloride monomer is made from a variety of different processestypically involving reaction of acetylene and hydrogen chloride or thedirect chlorination of ethylene. The polymerization is conventionallycarried out by radical polymerization of vinyl chloride. The PVC istypically combined with conventional polymer additives, including butnot limited to, impact modifiers, thermal stabilizers, lubricants,plasticizers, organic and inorganic pigments, fillers, biocides,processing aids, and flame retardants. The PVC can also be a copolymerof vinyl chloride monomer and one or more other copolymerizablemonomers. The copolymer can be any type of copolymer, including but notlimited to linear copolymers, block copolymers, graft copolymers, randomcopolymers, and regular repeating copolymers.

Suitable copolymerizable monomers that can be included in the PVC forthe present invention preferred embodiments include, but are not limitedto, acrylonitrile; alpha-olefins such as ethylene or propylene;chlorinated monomers, such as vinylidene dichloride; acrylate monomerssuch as acrylic acid, methyl acrylate, methyl methacrylate, acrylamide,and hydroxyethyl acrylate; styrenic monomers such as styrene, alphamethyl styrene or vinyl toluene; vinyl acetate; or any otherethylenically unsaturated copolymerizable comonomer. Preferably the PVCof the preferred embodiments is at least 50 wt % vinyl chloride monomerswith the remainder being one or more of the copolymerizable monomers.The PVC's used in the present composition can have a range of physicalproperties and can be alloyed or blended with other polymers as desired.Suitable alloying polymers include, but are not limited to ABS, acrylic,polyurethane and nitrile rubber. Such alloys or blends can provideimproved impact resistance, tear strength, resilience and/orprocessability.

In a preferred embodiment of the present invention, the resinousmaterial is rigid PVC, optionally containing a small amount ofplasticizer. The PVC is hard and tough and can be compounded to a widerange of properties, including impact resistance and weatherability(i.e. fading color to a wood grey appearance). The PVC preferably has atensile strength of about 6,000-7,500 psi, a percent elongation of about40-80%, and a tensile modulus of about 3.5-6.0×10⁶ psi. It can be usedwithout chlorination to about 140° F., and with chlorination to about220° F. It also has a coefficient of thermal expansion of about 3-6×10⁻⁵inch/inch-° F.

The composition of the present invention can be prepared by anyconventional polymer handling technique, including but not limited to,injection or vacuum molding, or extrusion and drawing. In a preferredembodiment, a mixture of PVC regrind and/or virgin PVC is compounded andthen heated and extruded through a die to produce boards and othershapes having any desired length, width and thickness, preferablylengths ranging from 4 to 20 feet and widths or thicknesses ranging from0.05 to 6.0 inches. The extruded products can be further processed bymolding, calendering and finishing to add surface textures or wood grainappearance.

The composition of the present invention further comprises a tannincontaining cellulosic material, preferably cellulosic fibers orcellulosic flours from recycled paper products, soft woods or hardwoods. More preferred cellulosic materials are those obtained from hardwoods due to their lower capacity to absorb moisture, with wood flourbeing more preferred and of these, oak flour being most preferred. Theoak flour is preferably of about 10-100 mesh, most preferably about20-30 mesh.

One or more additional fiber or flour type fillers can also be presentin the present invention composite, although in a preferred embodiment,the only such filler is the wood flour, preferably oak flour.

In a preferred embodiment, the resin and wood flour components arecombined with a chemical blowing agent, or a gaseous medium isintroduced into a molten mixture of the resin and wood fiber to producea series of trapped bubbles prior to thermo-forming the mixture, forexample, by molding, extrusion, or co-extrusion. These thermo-formingprocesses, as well as the methods for making foamed polymer articles arewell known in the art.

In a preferred process for making the composite of the presentinvention, a quantity of PVC (virgin and/or regrind) in small chunks ismixed with 20-30 mesh wood flour (preferably oak flour), which has beenpre-dried to release any trapped moisture as steam. The mixture also caninclude a melt enhancer, such as a high molecular weight acrylicmodifier, which improves melt elasticity and strength and enhancescellular structure, cell growth and distribution.

As noted above, the polymer composite of the present invention can befoamed by use of a chemical blowing agent or gas. Such a chemicalblowing agent or gas can be added to the mixture to reduce the densityand weight of the composite. The amount of blowing agent or gas is notparticularly limited. Preferably the blowing agent is added in an amountof from 0.5 to 1.5 phr (parts per hundred parts of polymer resin), morepreferably from 1.0 to 1.5 phr. This density reduction allows thecomposite product to better simulate wood in its ability to be nailed,drilled, and screwed. If a chemical blowing agent is used, it can beadded at any point during the process that is suitable for producing afoamed product. Preferably it is mixed into the compound during blendingor at the feed throat of the extruder. In the extruder, the blowingagent is decomposed, disbursing gas, such as nitrogen or carbon dioxide,into the melt. As the melt exits the extrusion die, the gas sitesexperience a pressure drop, expanding them into small cells or bubblestrapped by the surrounding polymer.

Chemical blowing agents useful in the present composition include anyconventional blowing agent which releases a gas upon thermaldecomposition. Chemical blowing agents may also be referred to asfoaming agents. The blowing agent, or agents, if more than one is used,can be preferably selected from chemicals containing decomposable groupssuch as azo, N-nitroso, carboxylate, carbonate, heterocyclic,nitrogen-containing and sulfonyl hydrazide groups. Generally, they aresolid materials that liberate gas when heated by means of a chemicalreaction or upon decomposition. Preferred blowing agents include, butare not limited to, azodicarbonamide, bicarbonates,dinitrosopentamethylene, tetramethylene tetramine,p,p′-oxy-bis(benzenesulfonyl)-hydrazide, benzene-1,3-disulfonylhydrazide, azo-bis(isobutyronitrile), biuret and urea.

The blowing agent can be added to the polymer in several different wayswhich are known to those of skill in the art. Suitable methods include,but are not limited to, adding the solid powder, liquid or gaseousagents directly to the resin in the extruder while the resin is in themolten state to obtain uniform dispersion of the agent in the moltenplastic or adding to the resin prior to entry into the extruder.Preferably the blowing agent is added before the extrusion process andis in the form of a solid. The temperature and pressure to which thefoamable composition of the invention are subjected to provide a foamedcomposition will vary within a wide range, depending upon the amount andtype of the foaming agent, resin, and cellulosic material that is used.Preferred foaming agents are selected from endothermic and exothermicvarieties, such as dinitrosopentamethylene tetrameine, p-toluenesulfonyl semicarbazide, 5-phenyltetrazole, calcium oxalate,trihydrazino-s-triazine, 5-phenyl-3,6-dihydro-1,3,4-oxadiazin-2-one,3,6-dihydro-5,6-diphenyl-1,3,4-oxadiazin-2-one, azodicarboamide, sodiumbicarbonate, and mixtures thereof.

The foamed composition of the preferred embodiments preferably has aspecific gravity of 1.25 g/cc or less, more preferably 1.20 g/cc orless, most preferably 1.07 g/cc or less. The porosity of the preferredembodiments preferably is at least about 1%, more preferably about 5-40%by volume of solids in the composite. Even though these specific gravityand porosity values provide a preferred product that is lightweight, thepreferred product has a flexural modulus, tensile modulus, and/orYoung's modulus of about 100,000 to 450,000 psi.

In addition to the above, a coloring agent can be added to thecompounded mixture, such as dyes, colored pigments, fly ash, carbonblack, or a mixture of two or more of these, depending on the resultingcolor desired and cost considerations. Such additives can provide“weatherability” or a faded greyish coloring or a permanent tint, suchas blue, green or brown.

The composite of the present invention further comprises calciumcarbonate as filler. The calcium carbonate can be contained in anyamount up to the point where the polymer fiber composite product losesits physical properties required for the desired end use. Preferably,the composite comprises up to 50 wt % of calcium carbonate (CaCO₃), morepreferably up to 15 wt %, most preferably up to about 5 wt %, based ontotal amount of composite. The calcium carbonate can be specificallyadded to the composition, or can result from the use of polymer resinregrind having calcium carbonate therein. Most regrind PVC containscalcium carbonate, up to about 5-8 wt %. Regrind sources that containcalcium carbonate include, but are not limited to, recycled vinylsiding, windows and pipes. Such regrind is desirable in the productionof polymeric wood substitutes since it lowers the cost, while little orno sacrifice in properties is observed. However, the presence of calciumcarbonate in such polymeric wood substitutes, particularly PVC woodsubstitutes that also contain wood fiber or wood filler, results instaining when the product is contacted with water. The water causestannins in the wood fiber or wood flour to leach to the surface andcause the appearance of unsightly stains.

Since the fiber material of the present invention contains tannins, itis necessary to add an amount of a stain preventive agent sufficient toprevent leaching and deposition of tannins from the cellulosic fiber tothe surface of the composite product upon contacting the product withwater. Tannins, within the context of the present invention, include anyof the series of compounds contained in cellulosic materials havingstructures similar to vescalagin, castalagin, grandinin, roburins A-E,portions of tannins such as lyxose, or xylose, as well as chemicalprecursors thereto, such as gallotannin, gallic acid, ellagitannin,hexahydroxydiphenic acid and ellagic acid (structures of these materialsare provided in FIGS. 1-3). Unfortunately, many tannins (lower molecularweight ones) are soluble in water, thus becoming solubilized andleaching to the surface of polymer-fiber composites when contacted withwater. This leaching and deposition on the surface of the productproduces unsightly brown stains on the surface of the product, having anegative impact on consumer satisfaction.

The stain preventive agent of the present invention is a compound thathas the ability to either couple two or more of these tannin moleculesto one another, couple a tannin molecule to a cellulosic unit in thecellulosic fiber itself, or both. This causes the tannins to lose theirsolubility and not be leached/deposited to the surface of the product,thus minimizing staining. The amount of stain preventive agent requiredis the amount sufficient to suppress the tannin leaching process. Thisamount will vary depending on the particular stain preventive agentused. The stain preventive agent is preferably a di (or higher)functional compound wherein the functionality has the ability to readilyreact with one or more of the hydroxyl groups present in the tanninscontained in the cellulosic fiber material. Preferred stain preventiveagents include, but are not limited to, organic di or polyacids andtheir anhydrides, preferably diacids and anhydrides, most preferablysuccinic acid, succinic anhydride, maleic acid, maleic anhydride,glutaric acid, glutaric anhydride, adipic acid, phthalic acid andphthalic anhydride. The amount of stain preventive agent is limited onlyby the tendency of the agent to plate out of the composition. Thisplate-out level varies depending on the particular agent and is readilydetermined by one of ordinary skill in the art. For example, the mostpreferred succinic anhydride tends to plate out at about 4 wt % based ontotal composition. Adipic acid tends to plate out at about 2 wt % basedon total composition.

Having generally described this invention, a further understanding canbe obtained by reference to certain specific examples which are providedherein for purposes of illustration only and are not intended to belimiting unless otherwise specified.

EXAMPLES

Varying Succinic Anhydride and Calcium Carbonate—A trial was performedusing a 35-mm extruder die and a PVC based polymer composition to whichwas added varying levels of succinic anhydride and calcium carbonate, todetermine the optimum level of succinic anhydride that is effective atlower calcium carbonate levels, corresponding to the use of PVC regrindwhich usually contains about 5-8 wt % of calcium carbonate. The PVCcomposition was conventional BOARDWALK® product from CertainTeedCorporation, a Saint-Gobain company, which contains about 62% compoundedPVC and about 38% of oak flour. The standard batch (1) was added to thehopper, with all other materials added manually to the extruder. Floodfeed conditions were maintained throughout.—

Approximately 8-inch samples representative samples from each formulavariation were cut and subjected to spot testing with distilled water.About 3 mLs of distilled water were placed on a surface of the sampleand permitted to dry for approximately 32 hours, after which the samplewas observed for visible staining.

The following compositions were prepared and tested, using Ross andHenschel mixers:

#1—Control, 11 kg boxed batch of PVC containing oak flour as notedabove, plus 66 g of Celogen® AZRV modified azodicarbonamide fromUniroyal Chemical Company, a Crompton business, as blowing agent.

#2—Composition #1 plus calcium carbonate equal to 1.3 wt % based on PVCcontent.

#2A —Composition #2 plus succinic anhydride equal to 0.16 wt % based ontotal composition.

#2B —Composition #2 plus succinic anhydride equal to 0.32 wt % based ontotal composition.

#3—Composition #1 plus calcium carbonate equal to 2.5 wt % based on PVCcontent.

#3A —Composition #3 plus succinic anhydride equal to 0.32 wt % based ontotal composition.

#3B —Composition #3 plus succinic anhydride equal to 0.6 wt % based ontotal composition.

#4—Composition #1 plus calcium carbonate equal to 5 wt % based on PVCcontent.

#4A —Composition #4 plus succinic anhydride equal to 0.6 wt % based ontotal composition.

#4B —Composition #4 plus succinic anhydride equal to 1.2 wt % based ontotal composition.

The results are shown in FIGS. 4-5.

The tests showed that the amount of succinic anhydride needed to beeffective at stain prevention varies directly as the amount of calciumcarbonate in the composition. When the amount of calcium carbonate islow, about 1.3% or less, there is no noticeable staining even withoutthe stain preventive agent. However, when the level of calcium carbonateincreased above about 1.3%, the level of succinic anhydride needed toprevent staining by tannins also increased, with about 0.32% succinicanhydride needed with about 2.5% calcium carbonate present, while about0.6% succinic anhydride was needed with about 5% calcium carbonatepresent.

Test of Addition of Succinic Anhydride to PVC/Oak Flour Product at 8 wt% Calcium Carbonate—A trial was performed using the same BOARDWALK®composition as in the above example, to which 8 wt % of calciumcarbonate (based on PVC content) was added to simulate the “worst case”scenario of using 100% regrind PVC. Three batches were tested —1) aControl batch containing 8 wt % calcium carbonate and no succinicanhydride; 2) a batch in which succinic anhydride was added to theControl to give total succinic anhydride level of 1.3 wt % based ontotal composition; and 3) a batch in which succinic anhydride was addedto the Control to give total succinic anhydride level of 1.92 wt % basedon total composition. Samples of each batch at room temperature weresubjected to the water staining test. In the test, two puddles were madeon each sample. One puddle was formed from a single 3 mL pipette ofwater, while the second puddle was formed using three 3 mL pipettes ofwater. After drying for 20 hours the samples were observed for staining.The Control batch showed dark spots for both single and triple squirtlocations, with the triple squirt location being nearly black inappearance. The 1.3 wt % succinic anhydride batch showed a very weakspot to no spot at all for the single squirt test, while the triplesquirt test showed staining, but considerably less than the Control. The1.9 wt % succinic anhydride batch showed virtually no stain in thesingle squirt test, and only minimal staining in the triple squirt test.Accordingly, even at the maximum level of calcium carbonatecorresponding to complete use of regrind PVC, the addition of thesuccinic anhydride showed significant improvements in stain prevention,particularly at levels of above 1.3 wt %.

Obviously, additional modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

1. A polymeric composite product, comprising: a polymer matrix; a tannincontaining cellulosic material; calcium carbonate; and an amount of acompound, having at least two functional groups capable of reacting withtannins present in said tannin containing cellulosic material,sufficient to prevent leaching and deposition of said tannins on asurface of the product when contacted with water.
 2. The polymericcomposite product of claim 1, wherein said polymer matrix is a polymerselected from the group consisting of thermoplastic and thermosettingresins.
 3. The polymeric composite product of claim 2, wherein saidpolymer matrix is a polymer selected from the group consisting ofpolyvinyl chloride (PVC), polyethylene, polypropylene, nylon,polyesters, polysulfones, polyphenylene oxide, polyphenylene sulfide,epoxies, cellulosics, and mixtures and blends thereof.
 4. The polymericcomposite product of claim 3, wherein said polymer matrix is PVC.
 5. Thepolymeric composite product of claim 1, wherein said tannin containingcellulosic material is a member selected from the group consisting ofcellulosic fibers and cellulosic flours.
 6. The polymeric compositeproduct of claim 4, wherein said tannin containing cellulosic materialis a member selected from the group consisting of cellulosic fibers andcellulosic flours obtained from a source selected from the groupconsisting of recycled papers, soft woods and hard woods.
 7. Thepolymeric composite product of claim 5, wherein said tannin containingcellulosic material is a wood flour.
 8. The polymeric composite productof claim 6, wherein said wood flour is oak flour.
 9. The polymericcomposite product of claim 1, wherein said compound having at least twofunctional groups is a member selected from organic diacids andanhydrides thereof.
 10. The polymeric composite product of claim 8,wherein said compound having at least two functional groups is a memberselected from the group consisting of succinic acid, succinic anhydride,maleic acid, maleic anhydride, glutaric acid, glutaric anhydride, adipicacid, phthalic acid and phthalic anhydride.
 11. The polymeric compositeproduct of claim 1, wherein said polymer matrix is PVC, said tannincontaining cellulosic material is oak flour and said compound having atleast two functional groups is succinic anhydride.
 12. A polymercomposite product, comprising: from 35 to 75 wt % of PVC; from 25 to 65wt % of oak flour; a non-zero amount of calcium carbonate up to about 15wt % based on PVC content; and from 0.1-5% of succinic anhydride.
 13. Amethod for preventing staining of polymeric composites, comprising:combining a polymeric composite product comprising a polymer matrix anda tannin-containing cellulosic material, with an amount of at least onecompound, having at least two functional groups capable of reacting withtannins present in said tannin containing cellulosic material,sufficient to prevent leaching and deposition of said tannins on asurface of the polymeric composite when contacted with water.
 14. Themethod of claim 13, wherein said combining step occurs in an extruderduring extrusion of said polymeric composite.
 15. The method of claim13, wherein said polymer matrix is a polymer selected from the groupconsisting of thermoplastic and thermosetting resins.
 16. The method ofclaim 15, wherein said polymer matrix is a polymer selected from thegroup consisting of, polyvinyl chloride (PVC), polyethylene,polypropylene, nylon, polyesters, polysulfones, polyphenylene oxide,polyphenylene sulfide, epoxies, cellulosics, and mixtures and blendsthereof.
 17. The method of claim 16, wherein said polymer matrix is PVC.18. The method of claim 13, wherein said tannin containing cellulosicmaterial is a member selected from the group consisting of cellulosicfibers and cellulosic flours.
 19. The method of claim 18, wherein saidtannin containing cellulosic material is a member selected from thegroup consisting of cellulosic fibers and cellulosic flours obtainedfrom a source selected from the group consisting of recycled papers,soft woods and hard woods.
 20. The method of claim 19, wherein saidtannin containing cellulosic material is a wood flour.
 21. The method ofclaim 20, wherein said wood flour is oak flour.
 22. The method of claim13, wherein said compound having at least two functional groups is amember selected from organic diacids and anhydrides.
 23. The method ofclaim 22, wherein said compound having at least two functional groups isa member selected from the group consisting of succinic acid, succinicanhydride, maleic acid, maleic anhydride, glutaric acid, glutaricanhydride, adipic acid, phthalic acid and phthalic anhydride.
 24. Themethod of claim 13, wherein said polymer matrix is PVC, said tannincontaining cellulosic material is oak flour and said compound having atleast two functional groups is succinic anhydride.